The claim was based on all branches of the British armed forces having only about 540 Muslims on the books, while estimates of "Brits" in ISIS range up to 1500.
The Guardian newspaper "rebuttal" was that no, many of the British Muslims in ISIS have been killed or returned home, so now there's probably slightly fewer than 500 UK nationals alive and in ISIS territory. IOW, Trump was basically correct, and Trump's main point, that the UK has a huge problem with its Muslim population - is 100 percent correct.
Thanks, guys....I was Navy, but the Riverine craft I served on didn’t carry nukes...*L*